Valves through which are passed liquids or gases mixed with small solid particles have the disadvantages that owing to the solid particles which tend to deposit on the sealing faces of the valve body and the seat, the valve cannot be properly closed, or in some instances the particles damage the sealing faces of the valve.
Constructions have been proposed which are so designed that the valve faces can be blown or flushed clean by means of an auxiliary gas or liquid. These constructions are, however, usually complicated and expensive. It has also been suggested to incorporate a filter so that the medium is filtered before passing the valve. The latter construction has admittedly the advantage that the clean medium flowing through the valve keeps the valve faces clean, but it has the disadvantage in that it is not intended to affect a blowing or flushing of the ceiling faces to dislodge any particles clinging thereto.